U.S. patent application number 10/205782 was filed with the patent office on 2003-02-27 for sensor apparatus and method for generating an output signal of a sensor apparatus.
Invention is credited to Draxelmayr, Dieter.
Application Number | 20030038623 10/205782 |
Document ID | / |
Family ID | 7629279 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038623 |
Kind Code |
A1 |
Draxelmayr, Dieter |
February 27, 2003 |
Sensor apparatus and method for generating an output signal of a
sensor apparatus
Abstract
The present invention provides a sensor apparatus having a
sensor (2) for generating an analog sensor signal (200) with
successive minima and maxima, and a corresponding method for
generating an output signal of a sensor apparatus. The apparatus is
provided with a first output signal generating device (4, 6, 7, 8,
9, 11, 23) for generating a first alternating output signal (5) in
accordance with the zero crossings of the sensor signal (200); a
sequence controller (25) for defining a normal operating phase, in
which the first output signal (5) can be output, and a calibration
phase, in which a second alternating output signal (5') can be
output; and an extremum defining device (16, 17) for the
phase-shifted definition of the successive minima and maxima; the
sequence controller (25) furthermore having a zero crossing
establishing device for establishing fictitious zero crossings of
the sensor signal (200) which follow the respective extrema defined
by the extremum defining device (16, 17); and a second output
signal generating device for generating the second alternating
output signal (5') in accordance with the fictitious zero crossings
of the sensor signal (200).
Inventors: |
Draxelmayr, Dieter;
(Villach, AT) |
Correspondence
Address: |
JENKINS & WILSON, PA
3100 TOWER BLVD
SUITE 1400
DURHAM
NC
27707
US
|
Family ID: |
7629279 |
Appl. No.: |
10/205782 |
Filed: |
July 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10205782 |
Jul 26, 2002 |
|
|
|
PCT/EP01/11296 |
Jan 11, 2001 |
|
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Current U.S.
Class: |
324/166 ;
324/173; 324/225 |
Current CPC
Class: |
G01D 18/001 20210501;
G01D 5/2448 20130101; G01D 18/008 20130101; G01D 5/2449
20130101 |
Class at
Publication: |
324/166 ;
324/173; 324/225 |
International
Class: |
G01P 003/48; G01R
033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2000 |
DE |
10004080.2 |
Claims
1. Sensor apparatus having: a sensor (2) for generating an analog
sensor signal (200) with successive minima and maxima; a first
output signal generating device (4, 6, 7, 8, 9, 11, 23) for
generating a first alternating output signal (5) in accordance with
the zero crossings of the sensor signal (200); a sequence
controller (25) for defining a normal operating phase, in which the
first output signal (5) can be output, and a calibration phase, in
which a second alternating output signal (5') can be output; and an
extremum defining device (16, 17) for the phase-shifted definition
of the successive minima and maxima; the sequence controller (25)
furthermore having: a zero crossing establishing device for
establishing fictitious zero crossings of the sensor signal (200)
which follow the respective extrema defined by the extremum
defining device (16, 17); and a second output signal generating
device for generating the second alternating output signal (5') in
accordance with the fictitious zero crossings of the sensor signal
(200); the first and second output signals (5, 5') being passed to
a changeover switch (30), which can be switched by a control signal
(ST), generated by the sequence controller (25), in such a way that
it supplies as output signal (A) the second output signal (5')
during the calibration phase and the first output signal (5) during
normal operation in the calibrated state.
2. Sensor apparatus according to claim 1, characterized in that the
zero crossing establishing device (25) is configured in such a way
that it establishes a fictitious zero crossing when the magnitude
of the amplitude of the sensor signal (200) has fallen by a
predetermined proportion after an extremum defined in a
phase-shifted manner.
3. Sensor apparatus according to claim 1 or 2, characterized in
that the extremum defining device (16, 17) determines the minima of
the analog sensor signal (200) as follows: successive storage of a
respective smallest value of the analog sensor signal (200) until
the difference in magnitude between a present larger signal value
and the smallest signal value stored last is greater than a
predetermined threshold; and if the difference in magnitude between
a present larger signal value and the smallest signal value stored
last is greater than a predetermined threshold, definition of the
smallest signal value stored last as minimum.
4. Sensor apparatus according to claim 1, 2 or 3, characterized in
that the extremum defining device (16, 17) determines the maxima of
the analog sensor signal (200) as follows: successive storage of a
respective largest value of the analog sensor signal (200) until
the difference in magnitude between a present smaller signal value
and the largest signal value stored last is greater than a
predetermined threshold; and if the difference in magnitude between
a present smaller signal value and the largest signal value stored
last is greater than the predetermined threshold, definition of the
largest signal value stored last as maximum.
5. Sensor apparatus according to one of the preceding claims,
characterized in that the second output signal generating device
(25) is configured in such a way that it determines a rotational
speed from the fictitious zero crossings established.
6. Sensor apparatus according to one of the preceding claims, the
analog sensor signal (200) having an AC voltage component and a DC
voltage component; and the first output signal generating device
(4, 6, 7, 8, 9, 11, 23) having a calibration device (7, 8, 9, 23)
for determining the DC voltage component of the analog sensor
signal (200) from the difference between successive minima and
maxima during the calibration phase.
7. Sensor apparatus according to claim 6, the first output signal
generating device (4, 6, 7, 8, 9, 11, 23) having a subtraction
device (6) for subtracting the DC voltage component determined from
the analog sensor signal (200) for the purpose of forming a
corrected analog sensor signal; and a comparator device (4) for
comparing the corrected analog sensor signal with a reference
signal and supplying a corresponding first output signal.
8. Method for generating an output signal of a sensor apparatus
having a sensor (2) for generating an analog sensor signal (200)
with successive minima and maxima, the method having the following
steps: definition of a normal operating phase, in which a first
alternating output signal (5) can be output in accordance with the
zero crossings of the sensor signal (200), and a calibration phase,
in which a second alternating output signal (5') can be output;
phase-shifted definition of the successive minima and maxima and
establishment of fictitious zero crossings of the sensor signal
(200) which follow the respective extrema defined in a
phase-shifted manner; and generation of the second alternating
output signal (5') in accordance with the fictitious zero crossings
of the sensor signal (200); the first and second output signals (5,
5') being passed to a changeover switch (30), which is switched in
such a way that it supplies as output signal (A) the second output
signal (5') during the calibration phase and the first output
signal (5) during normal operation in the calibrated state.
9. Method according to claim 8, characterized in that a fictitious
zero crossing is established when the magnitude of the amplitude of
the sensor signal (200) has fallen by a predetermined proportion
after an extremum defined in a phase-shifted manner.
10. Method according to claim 8 or 9, characterized in that the
minima of the analog sensor signal (200) are determined as follows:
successive storage of a respective smallest value of the analog
sensor signal (200) until the difference in magnitude between a
present larger signal value and the smallest signal value stored
last is greater than a predetermined threshold; and if the
difference in magnitude between a present larger signal value and
the smallest signal value stored last is greater than a
predetermined threshold, definition of the smallest signal value
stored last as minimum.
11. Method according to claim 8, 9 or 10, characterized in that the
maxima of the analog sensor signal (200) are determined as follows:
successive storage of a respective largest value of the analog
sensor signal (200) until the difference in magnitude between a
present smaller signal value and the largest signal value stored
last is greater than a predetermined threshold; and if the
difference in magnitude between a present smaller signal value and
the largest signal value stored last is greater than the
predetermined threshold, definition of the largest signal value
stored last as maximum.
Description
[0001] The present invention relates to a sensor apparatus and a
corresponding method for generating an output signal of a sensor
apparatus.
[0002] WO 99/42789 discloses an apparatus for detecting a passage
between a point on a body and a reference position. The apparatus
comprises a pair of magnetic field sensors, each of the sensors
generating an output signal based on the size of the magnetic field
which passes through the sensor. A difference-forming circuit is
provided which receives the output signals of the sensors and
generates a difference signal with a peak value when the point of
the body is positioned between the pair of sensors. Furthermore, a
peak value detector is provided which detects the peak value in the
difference signal. Moreover, the apparatus comprises a threshold
value circuit which receives the difference signal, for the purpose
of generating a gate signal if the magnitude of the difference
signal exceeds a threshold level, the gate signal enabling the peak
value pulse to be forwarded to an output terminal of the apparatus,
and preventing peak value pulses from being forwarded to the output
terminal of the apparatus in the absence of the gate signal.
Finally, the apparatus comprises a threshold value setting circuit
for setting the threshold value in accordance with the magnitude of
the difference signal.
[0003] DE 197 01 262 A1 discloses a detector for passing magnetic
articles with automatic gain control.
[0004] EP 0 642 029 A1 and EP 0 642 029 B1 disclose a
rise-activated Hall voltage sensor. This sensor comprises a circuit
branching device which is arranged in such a way that it follows a
positive rise, the subsequent positive peak value of the Hall
voltage is held at the detector output and the Hall voltage is
applied to a comparator, so that, if, after incipient impinging
[sic] of the Hall voltage from the positive maximum value, the
increasing difference between the Hall voltage and the held voltage
exceeds a predetermined magnitude, the resulting comparator output
pulse indicates the beginning of a variation in the strength of the
surrounding magnetic field at the Hall element.
[0005] Although applicable, in principle, to a wide variety of
sensor apparatuses, the present invention and the problem area on
which it is based are described with reference to a motor vehicle
crankshaft sensor.
[0006] As is known, sensors are used to detect the movement or the
positional state of rotating parts. Examples thereof are
crankshaft, cam shaft, transmission and ABS sensors in motor
vehicles. The sensors used are preferably Hall sensors which sense
the variations in a magnetic field. For this purpose, by way of
example, a permanent magnet is fitted to a stationary part in order
to generate a magnetic field. This magnetic field is then
modulated, depending on position, by a gearwheel fixed to the
rotating part or by another ferromagnetic transmitter. In this
case, the Hall sensor is preferably situated between the permanent
magnet and the gearwheel or transmitter and can thus detect
fluctuations in the magnetic field. By way of example, if a tooth
of the gearwheel lies in the magnetic field, then a "high" output
signal is supplied, while a gap between the teeth brings about a
"low" output signal. In this way, the instantaneous position or
annular velocity of a rotating part can be inferred from the signal
output by the Hall sensor.
[0007] The signal supplied by such a sensor is significantly
influenced by the operating conditions under which the sensor is
used. These operating conditions include unavoidable imponderables
such as, for example, operating temperature or size of the air gap,
etc. Despite the fluctuations caused by the operating conditions,
the sensor should supply an output signal that is defined as well
as possible. In other words, the output signal should have a
well-defined profile independently of the fluctuations caused by
the operating conditions. The reason for this is as follows: if a
sensor apparatus supplies a sinusoidal signal, for example, then a
well-defined behavior of a system disturbed by the sensor apparatus
can be obtained when switching operations in the system which
depend on the output signal of the sensor are performed at the zero
crossings of the signal. This is because these zero crossings are
independent of the respective signal amplitude and, moreover, have
a large edge steepness.
[0008] It goes without saying that a switching point other than
zero crossing or signal center may possibly also be advantageous in
the case of other signal waveforms of the output signal of the
sensor.
[0009] During the evaluation of the output signal of a sensor for
switching a system controlled by said sensor, a switching point
should thus be complied with independently of the signal amplitude
of the output signal of the sensor, which applies even to those low
signals. In detail, VDI Reports 1287, 1996, pages 583 to 611, "A
new generation of Hall-effect gearwheel sensors: advantages through
the combination of BIMOS technology and new packaging
formulations", describes a sensor arrangement in which firstly the
amplitude of the output signal of a sensor is normalized if
appropriate with the aid of an analog-to-digital converter. The
signal peak values are detected with the aid of two further
analog-to-digital converters and with digital-to-analog converters.
A switching threshold is derived and defined from said peak values.
In this way, finally, it is possible to achieve a system behavior
that is essentially independent of temperature fluctuations and the
width of the air gap. The outlay required for this sensor
arrangement is relatively high, however, since gain matching and
numerous analog-to-digital converters are required.
[0010] A circuit arrangement for calibrating switching points of a
decision unit driven by an analog input signal, independently of a
DC component contained in the input signal besides an AC component,
is known, the input signal having upper and lower signal peaks
which are in a selectable fixed ratio to one another. Provision is
made, in particular, of peak detectors for determining the upper
and lower signal peaks of the input signal; a controllable
reference unit for providing a reference signal; a computation unit
for determining the average value; a comparison unit; a regulating
unit for compensating for the DC component of the input signal and
a second regulating unit for oppositely tracking the reference
value, said second regulating unit being connected downstream of
the comparison unit on the input side and being connected to the
reference unit on the output side.
[0011] In particular, the output of the sensor apparatus is blocked
during the calibration phase. In the case of sensor apparatuses for
movement and position identification, however, it is often
important to correctly identify even small movements or the
beginning of a movement. In the case of sensors which do not
operate in a static manner, but rather operate by means of
filtering or self-calibration in order to obtain a higher accuracy,
the problem can arise, therefore, that, during the transient
recovery times, the system operates either only inaccurately or,
alternatively, not at all, so that the initial information is lost.
A known sensor apparatus needs, for example, a time of six zero
crossings until it supplies correct output information after the
conclusion of the calibration phase. The time through to that point
is required in order to set the internal circuit parameters in such
a way that the circuit has suitable operating points.
[0012] Static sensors without adaptation do not have this problem.
By the same token, they usually also have reduced sensitivity,
which restricts the range of use. Sensors with a filter can react
to the first or second zero crossing, but usually require a
relatively long time before the parameters have adapted to the
current operation to an extent such that the specified accuracy is
also achieved.
[0013] Therefore, it is an object of the present invention to
provide a sensor apparatus and a method for generating an output
signal of a sensor apparatus in which relatively reliable output
information can also be obtained during the calibration phase.
[0014] According to the invention, this object is achieved by means
of the sensor apparatus specified in claim 1 and the method
specified in claim 8.
[0015] The sensor apparatus according to the invention has the
advantage over the known solution approaches that there is no
system dead time during the calibration phase.
[0016] The idea on which the present invention is based consists in
the fact that, during the calibration phase, that is to say while
e.g. the circuit searches for minima and maxima for defining the
offset, the output information is not fundamentally blocked or
ignored, rather precisely these minima and maxima are utilized as
additional information sources.
[0017] More precisely, it is assumed that minima and maxima are
sought in a signal profile of such a sensor apparatus, while the
desire is to output an item of switching information at the signal
zero crossings, for example a switching to H for minima and a
switching to L for maxima. If a maximum has been found, then it can
be assumed that a negative zero crossing will now soon occur, while
in the event of a minimum being identified, it can be assumed that
a positive zero crossing will soon occur. The temporal offset
between the identification of the extrema and the actual zero
crossings is by its nature unknown in this case, but it is possible
in this way to generate a signal which indicates exactly the same
number of zero crossings as are actually contained in the original
signal.
[0018] Thus, the sensor apparatus based on this principle does not
operate particularly accurately with regard to phase angle, since a
maximum or a minimum is identified as such only if the actual
signal already deviates again considerably from the maximum value
or the minimum value. However, neither an item of information too
many nor an item of information too few is generated with regard to
the fictitious zero crossing, and therefore a distance covered per
unit time is reproduced correctly, namely by the time interval
between two adjacent fictitious zero crossings that are determined
in this way.
[0019] The subclaims contain advantageous developments and
improvements of the sensor apparatus specified in claim 1, and of
the method for generating a sensor signal as specified in claim
8.
[0020] In accordance with one preferred development, the zero
crossing establishing device is configured in such a way that it
establishes a fictitious zero crossing when the magnitude of the
amplitude of the sensor signal has fallen by a predetermined
proportion after an extremum defined in a phase-shifted manner.
[0021] In accordance with a further preferred development, the
extremum defining device determines the minima of the analog sensor
signal as follows: successive storage of a respective smallest
value of the analog sensor signal until the difference in magnitude
between a present larger signal value and the smallest signal value
stored last is greater than a predetermined threshold. If the
difference in magnitude between a present larger signal value and
the smallest signal value stored last is greater than a
predetermined threshold, definition of the smallest signal value
stored last as minimum.
[0022] In accordance with a further preferred development, the
extremum defining device determines the maxima of the analog signal
as follows: successive storage of a respective largest value of the
analog sensor signal until the difference in magnitude between a
present smaller signal value and the largest signal value stored
last is greater than a predetermined threshold. If the difference
in magnitude between a present smaller signal value and the largest
signal value stored last is greater than the predetermined
threshold, definition of the largest signal value stored last as
maximum.
[0023] In accordance with a further preferred development, the
second output signal generating device is configured in such a way
that it determines a rotational speed from the fictitious zero
crossings established.
[0024] In accordance with a further preferred development, the
analog sensor signal has an AC voltage component and a DC voltage
component. The first output signal generating device has a
calibration device for determining the DC voltage component of the
analog sensor signal from the difference between successive minima
and maxima during the calibration phase.
[0025] In accordance with a further preferred development, the
first output signal generating device has a subtraction device for
subtracting the DC voltage component determined from the analog
sensor signal for the purpose of forming a corrected analog sensor
signal; and a comparator device for comparing the corrected analog
sensor signal with a reference signal and supplying a corresponding
first output signal.
[0026] An exemplary embodiment of the present invention is
illustrated in the drawings and explained in more detail in the
description below.
[0027] FIG. 1 shows an illustration of a sensor apparatus for
elucidating an embodiment of the method according to the invention;
and
[0028] FIG. 2 shows a flow diagram of the embodiment of the method
according to the invention.
[0029] In the sensor apparatus illustrated in FIG. 1, the
rotational speed of a gearwheel 1 is detected by means of a Hall
sensor, subsequently amplified by means of an amplifier 3 and then
converted, with the aid of a comparator 4, into a pulse train whose
frequency corresponds to the rotational speed of the gearwheel 1.
The pulse train can then be tapped off at an output of the
comparator 4 as first output signal 5. By way of example by means
of [sic] magnetic DC fields acting on the Hall sensor 2 and/or
offset voltages in the amplifier 3 can lead to a DC signal being
superposed on an AC signal caused by the movement of the gearwheel
in the Hall sensor 2, which leads to the switching points of the
comparator 4 being shifted and, consequently, the pulse train of
the output signal 5 attaining a different duty ratio. However, this
corrupts the relationship between the pulse train of the output
signal 5 and the movement of the gearwheel 1.
[0030] In order to avoid this, in a known manner, a correction
signal determined in a particular manner is subtractively combined
with the output signal of the amplifier 3 in the comparator 4
acting as decision unit. This can also be achieved, moreover, for
example by correspondingly altering the switching threshold of the
comparator 4.
[0031] The correction signal is generated by means of a digital
control device 7, to which the output signal of the subtractor 6 is
fed with the interposition of a digitally controlled analog
amplifier 8 and an analog-to-digital converter 9. The
analog-to-digital converter 9 operates according to the tracking
principle. For this purpose, it has a subtractor 10, one input of
which is connected to the output of the amplifier 8. The output of
the subtractor 10 is connected to an input of a comparator 12, the
other input of which is connected to the reference-ground potential
11. The output of the comparator 12 is connected to the control
input of a counter 13, as a result of which the counting direction
of the counter is controlled. The counter 13 is additionally
connected up to a clock source 14. The counting result can be
tapped off at an output of the counter 13 and is fed at [sic]
binary word to a digital-to-analog converter 15, which generates a
corresponding analog signal from it. This analog signal is passed
to the subtractor 10, where it is subtracted from the output signal
of the controllable amplifier 8. Overall, the subtractor 10, the
comparator 12, the counter 13, the clock generator 14 and the
digital-to-analog converter 15 form an analog-to-digital converter
9 which operates according to the tracking principle. This means
that the binary word at the output of the counter 13 always follows
the output signal of the amplifier 8 in which [sic] the comparator
12, depending on whether the analog signal produced from the binary
word at the output of the counter 13 through the digital-to-analog
converter is greater or less than the signal at the output of the
amplifier 8, changes the counting direction of the counter 13 and
thus tracks the binary word to the signal at the output of the
amplifier.
[0032] The binary word at the output of the counter 13 is
additionally fed to two peak value detectors 16, 17, of which one
16 determines the relative minima and the other 17 determines the
relative maxima. The lower and upper signal peaks determined by way
of the relative minima and maximum are forwarded to a computation
unit 18 for calculation of the average value, which determines the
zero position of the input signal therefrom by averaging, for
example. This zero position is compared with a reference value by
means of a subtractor 19, which is connected downstream of the
computation unit 18. The reference value is provided by a reference
unit 20, which is likewise connected to the subtractor 19. In this
case, the reference value is altered by a reference control unit
21, which is connected upstream of the reference unit 20 and
downstream of the subtractor 19, in dependence in such a way that
the reference value is altered when the magnitude of the value of
the computation unit for the average value lies outside a specific
predetermined range.
[0033] The output of the subtractor 19 is additionally led to a
regulating unit 22, which, depending on the output signal at the
subtractor 19, generates a drive signal for the digital-to-analog
converter 23 connected downstream of it. In this case, the
regulating unit 22 generates a digital correction value which is
converted into an analog correction signal by the digital-to-analog
converter 23. Said correction signal is then subtracted from the
output signal of the amplifier 3 by means of the subtractor 6.
[0034] The control device 7 additionally receives a drive unit 24,
which is connected to the control input of the controllable
amplifier 8 on the output side and to the output of the counter 13
on the input side. The drive unit 24 may, for example, contain a
shift register whose content is formed by the binary word at the
output of the counter 13 and is controlled by it, thus resulting
overall in logarithmization of the binary word at the output of the
counter 13.
[0035] All the functions of the control device 7 are controlled by
a sequence controller 25. The sequence controller 25 is for the
[sic] connected to a timer 26 and a monitoring device 27 and to
various other components (indicated as double arrow in FIG. 1 for
simplification). On the input side, the monitoring device 27 is
connected to the output of the comparator 4 in order to monitor the
output 5 to the effect of whether it a signal change [sic] has
taken place within a specific time period prescribed by the timer
26. If no alteration is ascertained for this period of time, then a
new measurement of the DC component in the output signal of the
amplifier is carried out.
[0036] On the output side, the sequence controller supplies a
second output signal 5' and a control signal ST. The first and
second output signals 5, 5' are passed to a multiplexer or
changeover switch 30, which can be switched by the control signal
ST in such a way that it supplies as output signal A the second
output signal 5' during the calibration phase and the first output
signal 5 during normal operation, that is to say in the calibrated
state.
[0037] In order to generate the second output signal 5', the
sequence controller 25 contains an extremum defining device for the
phase-shifted definition of the successive minima and maxima on the
basis of the information of the peak value detectors 16, 17, and
also a zero crossing establishing device for establishing
fictitious zero crossings of the sensor signal 200 which follow the
respective extrema defined by the extremum defining device.
[0038] Furthermore, provision is made of a second output signal
generating device for generating the second alternating output
signal 5' in accordance with the fictitious zero crossings of the
sensor signal 200.
[0039] FIG. 2 shows a flow diagram of the embodiment of the method
according to the invention.
[0040] As stated, the second output signal 5' is present at the
system output A of the multiplexer 30, under the control of the
control signal ST, for as long as the calibration proceeds (step
100).
[0041] During the calibration, the digital signal values detected
by the control device 7 are examined for minima and maxima. In this
case, extrema are accepted as such only when they are sufficiently
greatly pronounced, i.e. a maximum is accepted as such only when
the signal subsequently becomes significantly smaller again. The
same applies correspondingly to minima. This condition affords
protection against a signal being simulated by noise or other
system disturbances. In particular, during the identification of
minima, a memory stores the smallest value found hitherto. If the
present value is greater than this value plus a safety margin
(noise margin), the stored value is interpreted as minimum (step
200).
[0042] In this example, the zero crossing establishing device is
configured in such a way that it establishes a fictitious zero
crossing when the magnitude of the amplitude of the sensor signal
200 has fallen by a predetermined proportion, e.g. in this case by
30%, after such an extremum (minimum in this case) defined in a
phase-shifted manner (step 300).
[0043] At the same time, the old maximum is erased and a new
maximum search is started. The maximum search functions
analogously. The largest value found hitherto is stored, and if the
present value has fallen to a sufficient extent, (safety margin),
the stored value is interpreted as maximum (step 400).
[0044] Once again the zero crossing establishing device establishes
a fictitious zero crossing when the magnitude of the amplitude of
the sensor signal 200 has fallen by a predetermined proportion,
e.g. in this case by 30%, after such an extremum (maximum in this
case) defined in a phase-shifted manner (step 500).
[0045] At the same time, a new minimum search is started.
[0046] Thus, during the calibration, zero crossings can be
continuously determined between respective adjacent pairs
minimum/maximum or maximum/minimum and a rotational speed, for
example, can be determined from the time interval between the zero
crossings.
[0047] This operating mode lasts (step 600-step 800) until the
calibration phase is concluded. A changeover is then made to the
normal calibrated operating mode (step 900), where the comparator 4
supplies the output signal 5 via the multiplexer 30 at the system
output A.
[0048] Although the present invention has been described above
using a preferred exemplary embodiment, it is not restricted
thereto, but rather can be modified in diverse ways.
[0049] In particular, the method according to the invention can be
used for a wide variety of sensor types.
[0050] The extrema determination, too, can, of course, take place
in a different manner than that shown.
[0051] Furthermore, the fictitious zero crossings can be
established by other methods, e.g. time control methods, event
control methods, or the like.
* * * * *